Forum for competition engine enthusiasts. RIP Guy Croft 09/11/2020 - This forum will continue both as a source of information and as a memorial to Guy.
My reading and understanding of the heading is as follows:
Is an estimate of the total heat rejected to the coolant that the radiator must deal with. This includes the heat energy which is lost to the coolant through the cylinder walls, combustion chamber walls and through the top of the piston plus the energy lost through the exhaust ports and from the friction heat generated from the internal moving parts expressed in horsepower. (Cooling designers can convert HP to BTU by multiplying by 2545)
An example taken form an computer program (used as guideline only and NOT as gospel) indications are that up to 63.9HP @ 8500RPM is lost through this process running at a hypothetical temperature of 80 degrees C.
Calculated 'Coolant HP loss'
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Taking your sound advice of running max of 75 deg C would mean that I would have to drop engine temp by at least 5 deg C. My question therefore is this: If I was able to reduce engine temp by 8 deg C or 10%, would that directly translate into a HP gain of equal percentage (10%) which then translates to a gain of 6.39Hp (4.76Kw) @ 8500RPM?
No, by using a lower temp stat or improved radiator etc you won't be reducing the gas-cylinder heat transfer & energy loss, you'll be lowering the metal temperatures and thus actually increasing it. The heat transfer to the coolant is proportional to the difference in gas-cylinder temperatures. Running cooler makes the specific fuel consumption higher but my own dyno tests have shown a net gain in power still comes from a significant reduction in charge temperature and increased density, formsay 86 to 75 deg C head temperature. Inducting at ambient helps still further.
The standard rule of thumb for IC engines is that the total available BTUs of the burn fuel; 1/3 goes to creating hp, 1/3 loss out the exhaust, and 1/3 loss due to heat transfer. This is the fundamental nature/design of the internal combustion engine. GC is correct manipulating the coolant temp does not have a direct affect on the HP. The one item that does is the loss of BTUs out the exhaust, these can be captured IE. turbos. Good discussion!